I am sorry to hear of the loss of your mother please accept my condolenses.
I think it is a wonderful idea to make a quilt out of her clothes. I am pretty new to quilting also so I really don't have any idea what you can use. I don't think that there is any "right" fabric or "wrong" fabric. Some people use flat sheets, some use cotton fabric, some even use muslin. I think its a preference. Someone will come along and give you an answer. :). You take care And God Bless you and your family. Cyber Hugs.